The hormone vasopressin is synthesized in hypothalamic neurons as pan of a precursor that also contains the disulfide-rich protein neurophysin and the glycopeptide copeptin. The self-association and hormone-binding properties of neurophysin play important roles in the targeting of vasopressin to neurosecretory granules and its storage within the granules. The function of copeptin is unknown. Familial neurogenic diabetes insipidus (FNDl) is a neurodegenerative disease typically caused by mutations in neurophysin. The disorder raises basic questions as to the structure and properties of the human vasopressin precursor, the structural basis of its normal fording and function, and the mechanisms by which mutations compromise these processes. The principal investigator has synthesized the cDNA encoding the human vasopressin precursor and propose to study the biophysical properties of the recombinant wild type protein and the effects of selected FNDI mutations on these properties. These studies have the potential to provide further insights into FNDI, as well as the first 3-dimensional structure of this precursor and the first view of copeptin structure and properties. The principal investigator proposes also to elucidate the basic mechanisms involved in neurophysin folding and function. The allosteric mechanism by which neurophysin dimerization is controlled by hormone-binding is an accessible paradigm for this process in other systems, and will be addressed here by NMR studies of the relative conformations of the unliganded monomeric and dimeric states and by the effects of targeted mutagenesis. Interrelationships among primary structure, disulfide pairing and folding, and between structure and binding, will be addressed by a series of studies that include investigation of the folding properties of isolated neurophysin domains and segments, and of the structural determinants of the strength of the critical salt bridge formed between hormone and protein.